Process of turning groups of animation nodes into templates for easy reuse?
A part of a node tree can be made reusable by encapsulating it in a subprogram, something analogous to functions in python. One can create multiple subprograms in a node tree and save it in an empty blend file, this file can act as a module where if one wants to use the subprograms defined there one would simply append the node tree previously defined. Note that subprograms can be invoked across node trees, so no further interaction from the user is required after appending the node tree.

If you want to go the extra mile and implement your own nodes in Animation Nodes using Python and Cython, have a look at the Developer's Guide.